Subsurface Profiling of Ion Migration and Swelling in Conducting Polymer Actuators with Modulated Electrochemical Atomic Force Microscopy

Understanding the dynamics of ion migration andvolume change is crucial to studying the functionality and long-term stability of soft polymeric materials operating at liquidinterfaces, but the subsurface characterization of swelling processesin these systems remains elusive. In this work, we address the issueusing modulated electrochemical atomic force microscopy as adepth-sensitive technique to study electroswelling effects in thehigh-performance actuator material polypyrrole doped withdodecylbenzenesulfonate (Ppy:DBS). We perform multidimen-sional measurements combining local electroswelling and electro-chemical impedance spectroscopies on microstructured Ppy:DBSactuators. We interpret charge accumulation in the polymericmatrix with a quantitative model, giving access to both thespatiotemporal dynamics of ion migration and the distribution of electroswelling in the electroactive polymer layer. The findingsdemonstrate a nonuniform distribution of the effective ionic volume in the Ppy:DBS layer depending on the film morphology andredox state. Our findings indicate that the highly efficient actuation performance of Ppy:DBS is caused by rearrangements of thepolymer microstructure induced by charge accumulation in the soft polymeric matrix, increasing the effective ionic volume in thebulk of the electroactive film for up to two times the value measured in free water.